Senate Democrats are requesting an FTC investigation into “potential price fixing” of gasoline by petroleum refiners.

The Democrats — including Senate Majority Leader Harry Reid and other Senate Democratic leaders — say refiners may be “cutting back on U.S. gasoline stockpiles in order to artificially keep prices high and inflate their bottom line,” according to a draft letter to FTC Chairman Jon Leibowitz. “If true, this behavior is a direct affront to the American people who are still struggling with the economic downturn.”

They add: “At a time when major refiners and oil companies are making record profits and American families continue to struggle with gasoline at record prices, the idea that refiners may be manipulating the market to keep prices artificially high goes beyond reproach.”

John Felmy, chief economist at the American Petroleum Institute, dismissed the call for a probe as "kind of like the 'Casablanca' moment; you know, round up the usual suspects."

McCaskill — who is one of the biggest targets for Republicans in 2012 — has also been given a leading role by Senate Democratic leaders on legislation up for vote Tuesday that would raise taxes for the five biggest private integrated oil companies by $21 billion over 10 years and steer those dollars toward reducing the deficit.

Democratic leaders know that bill will not get the needed 60 votes today during an initial procedural vote.

But the aim is to give McCaskill — who has been under fire for back taxes owed and other issues regarding a private plane she co-owned with her husband — and other vulnerable Senate Democrats some talking points heading into the thick of their campaigns.

While Senate Democratic leaders have acknowledged that the bill repealing oil industry tax incentives will do nothing to lower gas prices, much of their eyebrow raising over soaring prices at the gas pump has been aimed at excessive speculation in oil markets and potential price manipulation.

“The rise in the price of oil is certainly a driving factor behind the recent rise in gasoline prices, but concerns have been raised that while gasoline use is declining, U.S. gasoline inventories remain below average and refining margins continue to rise,” the Democrats say in the draft letter to Leibowitz.

They cite data from the Energy Information Administration — the independent research arm of the Energy Department — stating that U.S. refiners are using about 82 percent of their capacity, down 7 percent from this time last year.

Felmy said refinery capacity is a bad measure and that refineries are producing record amounts of gasoline. "The key thing you want to focus on is how much comes out of a refinery," Felmy said. "And you can’t argue that refiners are trying to manipulate things when they’re producing record production."

Refining margins have also gone up 90 percent since the start of the year, the Democrats said. Refining margins are the difference in value between the products produced by a refinery and the value of the crude oil used to produce them and generally tend to go up when crude oil prices rise.

Oil industry officials contend that refiners struggled last year and that higher margins are due to supply and demand and reaction to flooding along the Mississippi River.

The Democrats contend that the flooding alone "cannot justify the steady increases in their margins since January of this year."

This article first appeared on POLITICO Pro at 9:36 a.m. on May 17, 2011.